Cathode ray tube



w 1940- E. STEUDEL QCATHODE RAY TUBE Filed Dec. 11. 1937 INVENTOREBERHAPD STEUDEL BY f6? ATTORNEY Patented Sept. 17, 1940 UNITED STATESCATHODE RAY T'UBE Eberhard Steudel, Berlin-Dahlem, Germany, assignor toGeneral Electric Company, a corporation of New York Application December11, 1937, Serial N 0. 179,232 In Germany December 16, 1936 3 Claims.

The "invention is concerned with an arrangement for a'Braun tube whichmakes it feasible to operate the tube on lower potentials thanheretofore customary, Without losing any of the glow or luminosityintensity, while making brief actions visible for a prolonged period oftime. What is used for this purpose is an electrode of the kind known inthe art of television. This electrode or screen plate may be made in thefollowing manner:

A metal gauze or network is oxidized with the result that theconstituent wires of the reticular structure are covered with aninsulating coat or film. Next metal is brought into the interstices orgaps between the Wires of the gauze in some suitable manner so that theentire screen plate eventually becomes a mosaic comprising amultiplicity of metal particles individually insulated from one another,the said metallic particles extending from the anterior face to theposterior face of theelectrode. Thus, if a charged pattern is focusedupon the anterior face of the screen plate, the same patternof chargeswill appear also upon the posterior face thereof.

According to this invention, such a screen plate is used in a Braun orcathode-ray tube, the said screen plate being provided on one facethereof, that is, the posterior face, with a substance which is causedto luminesce when bombarded by electrons. The said luminiscent orfluorescent substance is applied preferably upon such spots of thesurface or plate where the insulating grid wires are located so that theso-called electrode or metallic particles will stay bare, that is, willnot be coated by the luminescent substance. Now, a Braun tube accordingto the invention is operated in such a way that upon the anterior faceof the electrode, in the usual way, an oscillographic tracing appears,whereas the posterior face thereof is bombarded by an intense anduniform electron pencil being inherently homogeneous.

Now, a Braun tube of this design and type operates in the followingfashion: Since the elements upon the anterior face of the screen platewhich correspond to the action to be outlined (oscillogram) arenegatively charged by the electron pencil of the cathode-ray tube, theuniform cathode-ray pencil which falls upon the posterior face of theelectrode will be kept away wholly or partly from these elements,whereas it will excite the luminescent substances of the other elements.In other words, what is obtained is the negative of an otherwisecustomary tracing.

A Braun or cathode-ray tube as here disclosed offers the advantage thatfor both cathode-ray beams, that is, for the pencilfalling upon theanterior face of theelectrode, and the auxiliary pencil which wouldcause homogeneous glow or illumination upon the posterior face of thescreen plate or electrode, only comparatively low potentials arerequired. The delineator or tracing pencil is not in need of a highvoltage since it serves solely for the charging of the elements of thescreen plate, for it is not called upon to excite the luminescentsubstance as is usually the case. The auxiliary pencil, on the otherhand, which is not subject to control actions and which need not befocused is not required to pass through high voltage. \Vhile it is truethat the said auxiliary pencil is required to excite the luminescentsubstance, it will result in the requisite luminosity or brilliance byhigher pencil density. The fact that no high potential is required forthetracing pencil insures at the same time high sensitivity for the tubewithout it being necessary to provide special steps and means such asspace-charge diaphragms or apertures, and supplemental or re-acceleratormeans' Due to the further circumstance that the luminescent screen maybe viewed in plan or directly such losses as are usually caused by lightabsorption inside the layer are obviated.

Finally, persistence of image or pattern beyond the instant of tracingaction is insured because of the fact that the distribution of thecharges throughout the pattern is non-instantaneous, and this is anadvantageous feature which proves particularly valuable in the tracingof high-speed non-recurrent actions or phenomena as in connection withthe use of Braun tubes in television work.

The screen plate itself can be manufactured by extremely simple methodssince neither the recording or tracing pencil nor the auxiliary pencilare required to penetrate through the screen plate so that no specialprecautionary measures are needed to preclude undue thickness of themetallic inserts.

Figure l of the drawings illustrates, by way of example, a screen-plateaccording to this invention in several stages of its manufacture.

Figure 2 shows a Braun tube fitted with a raster or screen-plate of thekind shown in Figure 1. 5O

Numeral I denotes the metallic network, gauze or grid which is coatedwith an insulation film 2. In the interstitial spaces or meshes betweenthe grid wires are placed the metal particles indicated by 3. Theluminescent substance which posteriorly is applied preferably only uponthe insulation portions is designated by 4.

In Figure 2, I0 denotes the screen plate and opposite the anterior facethereof is a source of electrons. The said source consists here of adirectly heated cathode iii. For focusing the electron pencil areprovided the intermediary partitions or diaphragms l3, intermediatecylinder M, the anode diaphragms or apertures l5, while the intensity ofthe pencil is regulated or modulated by the potential impressed upon theaperture plate l6. Numerals I1 and I8 denote pencil deflector means. Theposterior of the screen-plate ll] which is covered with luminescentsubstances is bombarded by a homogeneous electron pencil generated bythe source of electrons l9 and the condensing device 20, 2! (electricimmersion objective).

Viewing may be in the direction of the arrow 22, but if oblique viewingof the screen is to be avoided, then the ray generating means I9, 20, 2]may be so mounted that the homogeneous pencil of electrons will becaused to strike the screen-plate or raster H] obliquely,-say, roughlyin the sense of the arrow 22, with the result that the observation ofthe recording of the luminescent-screen pattern will be at right anglesto the screen. Even when the axes of the auxiliary electron source areinclined in reference to the normal to the screen-plate, obliquebombardment with electrons may be avoided by ways and means known in theprior art, that is, by the aid of a magnetic field which is positionedat right angles to the normal to the screen-plate and the axis of theauxiliary electron source.

The leads for current and potential have not been included in thedrawing, but it is to be understood that for screen-plate I 0 in a casewhere the usual current drain by way of the walls of the vessel shouldprove inadequate, a distinct and separate voltage or current returnconductor may be provided to restore the screen-plate to its quiescentor normal potential value after bombardment with electrons has beenfinished.

thereof comprising a fine mesh screen, a layer of insulation, completelycovering said screen, conducting members in the interstices of saidscreen, and a fluorescent coating deposited only on the insulation andonly on the side of the screen toward said flooding source of electrons.2.. A cathode ray tube comprising an envelope,-

an electrode positioned intermediate the ends of the envelope and normalto the axis thereof, said electrode comprising a fine mesh screen, alayer of insulation completely covering said screen, conducting membersin the interstices of said screen, a fluorescent coating deposited onlyon the exposed insulation and only on one side.

of said screen, means in one end of said envelope adapted to produce auniform field of flooding electrons and for directing the producedelectrons against said one side of the screen, and means at the otherend of said envelope adapted to produce a narrow beam of low velocityelectrons for systematically scanning the other surface of said screen.

. 3. An electrode member comprising a fine mesh screen grid ofconducting elements, a layer of insulation deposited upon each elementof said grid, conducting material positioned in the interstices of thescreen between each of the grid elements and separated by the insulationon said elements, and a fluorescent coating deposited only on theinsulation and only on one side of each of the grid elements to theexclusion of the conducting elements positioned between said elements.

' EBERHARD STEUDEL.

